Imaging devices used in, for example, portable telephones and automobiles are required to have excellent performance stability and durability at high and low temperatures, and other harsh environmental conditions. Accordingly, Patent Literatures 1 and 2, for example, propose using a ceramic lens barrel. Patent Literature 3 proposes using porous ceramic excelling in air permeability and durability for optical parts.
A lens barrel part generally comprises, as described in, for example, Patent Literature 4, a lens barrel body containing a plurality of lenses, spacing rings for defining the distances between the lenses in the lens barrel body, and a holder ring provided at an end of the lens barrel body. The lenses incorporated in the lens barrel part are in contact with the lens barrel body and thus secured to ensure that the optical axes and focal points of the lenses remain in alignment. On the other hand, a lens barrel part of porous ceramic generally has fine asperities on the surfaces thereof. Therefore, a problem may arise that when, for example, lenses are placed in the lens barrel part, the friction between lenses and the part produces grinding debris from the lens barrel part.
On the other hand, Patent Literature 5, for example, proposes coating the whole surface of a ceramic with a protection film by tribochemical reaction to smooth the surface.